Does Hounsfield Unit have any significance in predicting intra and postoperative outcomes in retrograde intrarenal surgery using holmium and Thulium fiber laser? A critical analysis of results from the FLEXible ureteroscopy Outcomes Registry (FLEXOR)

Abstract

Abstract The objective was to evaluate outcomes of retrograde renal surgery for intrarenal stones of any size, number, and position, comparing hard versus soft stones based on their attenuation on computed tomography (Hounsfield Unit-HU). Exclusion criteria; children/adolescents, ureteric stones, renal anomalies, or bilateral surgery. Patients were divided into two groups according to the type of laser employed, i.e. Holmium:YAG (HL) and Thulium fiber laser (TFL). Residual fragments (RF) were defined as > 2 mm. Multivariable logistic regression analysis was performed to evaluate factors associated with RF and RF needing further intervention. 4208 patients from 20 centers were included. 3070 patients were operated on with HL. In HU < 1000 stones, the TFL group had larger stones (11.56 ± 10.38 vs 9.98 ± 6.89 mm,p < 0.001). Multiple and lower pole stones were more prevalent in the HL group. Lasing time was shorter in the TFL group (15.34 ± 12.55 vs 23.32 ± 15.66 minutes,p < 0.001). HL group had a higher incidence of RF (29.1% vs 13.7%,p < 0.001). Age, stone size, and HL were predictors of RF, whereas multiple stones, and HL of RF requiring retreatment. In HU ≥ 1000 stones, stone size was similar between the two groups, whilst multiple and lower pole stones were more prevalent in the HL group. Surgical time was significantly shorter in the HL group (64.48 ± 33.92 vs 79.54 ± 88.56,p < 0.001). Significantly higher incidence of RF was noted in HL (22.7% vs 9.8%,p < 0.001), whilst reintervention rate was significantly higher TFL group (69.6% vs 43.8%,p < 0.001). Age, stone size, and use of HL were predictors of RF, whilst recurrent stone formers, multiple stones, and use of TFL of RF requiring retreatment.